The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates to methods and apparatuses for cooling electronic components and other objects, more particularly to such methods and apparatuses involving removal, absorption and/or dissipation of heat.
A xe2x80x9cheat sinkxe2x80x9d (alternatively spelled xe2x80x9cheatsinkxe2x80x9d) is a device used for removing, absorbing and/or dissipating heat from a thermal system. Generally speaking, conventional heat sinks are founded on well known physical principles pertaining to heat transference. Heat transference concerns the transfer of heat (thermal energy) via conduction, convection, radiation or some combination thereof. In general, heat transfer involves the movement of heat from one body (solid, liquid, gas or some combination thereof) to another body (solid, liquid, gas or some combination thereof).
The term xe2x80x9cconductionxe2x80x9d (or xe2x80x9cheat conductionxe2x80x9d or xe2x80x9cthermal conductionxe2x80x9d) refers to the transmission of heat via (through) a medium, without movement of the medium itself, and normally from a region of higher temperature to a region of lower temperature. xe2x80x9cConvectionxe2x80x9d (or xe2x80x9cheat convectionxe2x80x9d or xe2x80x9cthermal convectionxe2x80x9d) is distinguishable from conduction and refers to the transport of heat by a moving fluid which is in contact with a heated body. According to convection, heat is transferred, by movement of the fluid itself, from one part of a fluid to another part of the fluid. xe2x80x9cRadiationxe2x80x9d (or xe2x80x9cheat radiationxe2x80x9d or xe2x80x9cthermal radiationxe2x80x9d) refers to the emission and propagation of waves or particles of heat. The three heat transference mechanisms (conduction, convection and radiation) can be described by the relationships briefly discussed immediately hereinbelow.
Conductive heat transfer, which is based upon the ability of a solid material to conduct heat therethrough, is expressed by the equation q=kAxcex94T/l, wherein: q=the rate of heat transfer (typically expressed in watts) from a higher temperature region to a lower temperature region which is in contact with the higher temperature region; k=the conduction coefficient or conductivity (w/m-c), which is a characteristic of the material composition; A=the surface area (m2) of the material perpendicular to the direction of heat flow; xcex94T=the temperature difference (xc2x0 C.), e.g., the amount of temperature drop between the higher temperature region and the lower temperature region; and l=length (m) of the thermal path through which the heat is to flow (e.g., material thickness).
Convective heat transfer, which is based upon the ability of a replenishable fluid (e.g., air or water) to absorb heat energy through intimate contact with a higher temperature solid surface, is expressed by the equation q=hAxcex94T, wherein: h=the fluid convection coefficient (w/m2xe2x88x92xc2x0 C.), wherein h is determined by factors including the fluid""s composition, temperature, velocity and turbulence; and, A=the surface area (m2) which is in contact with the fluid.
Radiative heat transfer, which is based upon the ability of a solid material to emit or absorb energy waves or particles from a solid surface to fluid molecules or to different temperature solid surfaces, is expressed by the equation q=Axcex5{haeck over (o)}(Ts4xe2x88x92T∞4), wherein: xcex5=the dimensionless emissivity coefficient of a solid surface, characteristic of the material surface; {haeck over (o)}=the Stefan-Boltzmann constant; A=the surface area (m2) which radiates heat; Ts=absolute temperature of the surface (K); and, T∞=absolute temperature of the surrounding environment (K).
It is theoretically understood that, regardless of the heat transfer mechanism, heat transfer rate q can be increased by increasing one or more factors on the right side of the equationxe2x80x94viz., the heat transfer coefficient (k, h or E), and/or the (surface or cross-sectional) area A and/or the temperature reduction xcex94Txe2x80x94and/or by reducing the path length l.
In current practical contexts, heat sinks generally are designed with a view toward furthering the conductive properties of the heat sink by augmenting or optimizing the conduction coefficient k, the surface area A and the path length l. Conduction coefficient k depends on the materiality of the heat sink. In this regard, according to conventional practice, a heat sink structure is made of a thermally conductive solid material, thereby maximizing the conduction coefficient k characteristic of the heat sink. In addition, the heat sink structure tends to be rendered large (e.g., bulky or voluminous), especially the portion thereof which contacts the to-be-cooled body, thereby maximizing the cross-sectional area A or minimizing the path length l which are design characteristic of the heat sink.
Generally speaking, the materials conventionally used in the industry for heat sink manufacture are characterized by high heat conductivity and low weight. These materials are usually a metal or metal alloy. The most common materials used in the manufacture of heat sinks are aluminum and copper. These materials are often coated with nickel or another finish to prevent corrosion. Metal alloy materials are also finding their way into the mainstream of heat sink design, provided they have a high thermal conductivity and a low weight.
All conventional heat sinks which have been observed, including those which are commercially available, effectuate some form of conductive heat transfer, and are primarily dependent thereon or governed thereby. Conventional heat sinks mainly rely on heat conduction through a solid-on-solid contacting interface between the tobe-cooled object and the heat sink device. These conventional devices are typically fabricated from a high heat-conducting material, generally a metallic material.
Many conventional heat sinks feature various arrangements and configurations of protrusive structuring (e.g., pins, fins, pins-and-fins, mazes, etc.) which are intended to increase the heat sink""s size parameters (cross-sectional area A), thereby increasing the amount of conductive heat transfer surface (i.e., the amount of conductive heat dissipation/removal). The protrusive structuring is rendered to be thermally conductive and to increase the overall heat transfer coefficient the heat sink.
Some of these conventional devices implement cooling fluid flow (e.g., water or air) which passes through the heat sink""s protrusive structure or structures, or which otherwise contacts solid material of the heat sink. In all such known applications, the heat sink is adapted to first being thermally conductive, and the fluid is adapted to then being thermally convective with respect to heat which has previously been thermally conducted by the heat sink.
Typically in conventional practice, a sizable mass (e.g., a block) of a thermally conductive solid substance (e.g., a metallic material) is placed in direct contact with the high temperature body. Nevertheless, heat sink applications involving a high power density (i.e., high heat flux, or high heat dissipation over a small surface area) do not ideally lend themselves to a cooling methodology wherein a thermally conductive material directly contacts a body which operates at a high power density. Some of the potential detriment stems from the normal circumstance that the thermally conductive material is metallic.
Metals are characterized by the presence of relatively free electrons, and hence are characterized by high thermal conductivity as well as high electrical conductivity. There exists a relation between the thermal conductivity of a metal to its electrical conductivity; pursuant to the Wiedemann-Franz law, for instance, the ratio of the thermal conductivity of any pure metal to its electrical conductivity is about the same at the same given temperature. As pertains to conventional heat sink practice, the thermally conductive material which is implemented generally will be a metal and therefore will also be electrically conductive.
Thus, there are potential problems associated with conventional approaches to effectuating heat sink cooling of an entity behaving at a high power density. First of all, a conventional heat sink arrangement will usually demand a large amount of thermally conductive material in order to dissipate the heat. Moreover, the thermally conductive material is typically metallic and hence is subject to corrosion from its environment. The corrosive influence may be heightened when the metallic material comes into contact with a liquid. In addition, the electrically conductive nature of the metallic material promotes the corrosiveness thereof through electrochemical means, particularly when contacting a liquid. Furthermore, some cooling applications require or preferably implement electrically nonconductive material in the heat sink. For instance, the electrically conductive heat sink material can pose a short-circuitry risk or otherwise represent an electrical threat or hazard.
The United States Navy recently encountered a situation which revealed some deficiencies of conventional heat sink technology. The Naval Surface Warfare Center, Carderock Division, took part in a research and development program for power electronics, known as the xe2x80x9cPEBBxe2x80x9d program. The letters xe2x80x9cPEBBxe2x80x9d acronymously represent xe2x80x9cPower Electronics Building Block.xe2x80x9d A PEBB has been described as a xe2x80x9cuniversal power processorxe2x80x9d; that is, a PEBB can change any electrical power input to any desired form of voltage, current and frequency output. The U.S. Government and U.S. industry are jointly participating in a PEBB program for developing a new family of semiconductor devices for the power electronic industry. An objective of the PEBB program is to promote modularization and standardization to power electronics, similarly as has been accomplished in the realm of computers and microchips.
Demonstration power conversion units were to be produced by the U.S. Navy, according to this PEBB program. These demonstration units were to utilize power modules developed as part of this program by a commercial semiconductor manufacturer. These developmental modules were required to operate at high power densities. The semiconductor devices were to be mounted to a dielectric (electrically nonconductive) baseplate, typically manufactured from ceramic materials, which is subject to breakage when a module fails.
It was therefore necessary, in this PEBB R and D program, for the U.S. Navy to effectuate heat dissipation/removal technology which would satisfy certain criteria. Firstly, in order to be feasible for shipboard applications, the size and weight of the power electronic module and its corresponding heat sink apparatus had to be kept to a minimum.
Environmental factors had to be considered; for example, utilization of chemicals for heat dissipation could be hazardous in a shipboard environment. Uniform cooling and mechanical support had to be provided, within the heat sink, to the ceramic baseplate. Low manufacture and assembly costs were also important issues. High reliability and low maintainability were important issues, as well.
A notable inadequacy of current heat sink technologies is their inability to satisfactorily afford mechanical support to certain entities, particularly to dielectric materials (such as ceramic materials) characterized by brittleness and by lower thermal conductivity than most metals. According to current state-of-the-art heat sink devices, mechanical support is provided within the metallic (metal or metal alloy) materials which are used to conduct the heat through the heat sink device. Aside from the size and weight penalties characteristic of these current devices, they will also be subject to the inefficiencies and high costs associated with attachment of the ceramic baseplate to the metallic heat sink device.
Of interest in the art are the following United States patents, each of which is hereby incorporated herein by reference: Kikuchi et al. U.S. Pat. No. 5,894,882 issued Apr. 20, 1999; Lavochkin U.S. Pat. No. 5,829 516 issued Nov. 3, 1999; Romero et al. U.S. Pat. No. 5,666,269 issued Sep. 9, 1997; Mizuno et al. U.S. Pat. No. 5,522,452 issued Jun. 4, 1999; Agonafer et al. U.S. Pat. No. 5,482,113 issued Jan. 9, 1996; Agonafer et al. U.S. Pat. No. 5,370,178 issued Dec. 6, 1994; Reichard U.S. Pat. No. 5,316,077 issued May 31, 1994; Iversen et al. U.S. Pat. No. 4,989,070 issued Jan. 29, 1991; Iversen U.S. Pat. No. 4,712,609 issued Dec. 15, 1987; Klein U.S. Pat. No. 4,521,170 issued Jun. 4, 1985; Missman et al. U.S. Pat. No. 3,912,001 issued Oct. 14, 1975.
In view of the foregoing, it is an object of the present invention to provide heat sink method and apparatus which are capable of dissipating/removing heat from a device or other to-be-cooled object which is characterized by a high power density.
It is another object of the present invention to provide heat sink method and apparatus which are capable of providing mechanical support for a to-be-cooled object.
Another object of this invention is to provide such supportively capable method and apparatus which can provide mechanical support for a to-be-cooled object (such as a module) having a baseplate, providing such mechanical support by supporting the baseplate, especially when the baseplate is made of a brittle material such as ceramic.
A further object of this invention is to provide heat sink method and apparatus which provides cooling, for a to-be-cooled object (such as a module) having a baseplate, wherein the cooling is uniform over the entire surface area of the baseplate.
Another object of the present invention is to provide heat sink method and apparatus which are not large, cumbersome or heavy.
A further object of this invention is to provide heat sink method and apparatus wherein the heat sink admits of being made of a material which is at least substantially noncorrosive.
Another object of this invention is to provide heat sink method and apparatus wherein the heat sink admits of being made of a material which is at least substantially dielectric.
A further object of the present invention is to provide heat sink method and apparatus which are environmentally xe2x80x9cfriendly.xe2x80x9d
The present invention provides a heat sink for cooling an object, and a methodology for accomplishing same. The inventive heat sink is capable of being used in association with a fluid (liquid or gas) for effectuating cooling. Either liquid coolant or gas coolant can be used in inventive practice.
This invention is especially propitious for cooling an object such as a power electronic module having a flat (e.g., ceramic) baseplate which is susceptible to breakage in the event of a module failure. Featured by the present invention is direct contact of a coolant (e.g., water) stream with the high temperature object being cooled.
The present invention further features turbulence enhancement of the coolant stream by a pin array through which the coolant stream passes. According to many embodiments, this invention additionally features the affording of mechanical support of the object being cooled, while maintaining high heat flux cooling of such object (e.g., a power electronic module); the invention""s pins are upright, post-like members which act as supporting structures.
In accordance with many embodiments of the present invention, a heat sink device for utilization in association with fluid for cooling an object comprises a structure which includes a foundation section and plural protrusions. The foundation section has an upper surface. The protrusions are situated on the upper surface. The structure is adaptable to engagement with the object and to association with the fluid wherein: the object and some or all of the protrusions touch; and, the fluid streams approximately tangentially with respect to the upper surface and with respect to the object. According to typical inventive practice, the structure is adaptable to such engagement and association wherein at least one protrusion affects the streaming of the fluidxe2x80x94more typically, wherein plural protrusions, which are some or all of the protrusions, affect the streaming of the fluid.
The inventive cooling apparatus is for application to any bodyxe2x80x94for example, an electronic circuitry device or other electronic component.
The inventive fluid-cooling heat sink apparatus typically comprises fluidity means (e.g., a fluid generation system) and a member. The subject body has a body surface portion. The member has a member surface portion and a plurality of pins projecting therefrom. According to frequent inventive practice the pins are approximately parallel; however, such parallelness is not required in accordance with the present invention. Each pin has a pin end surface portion opposite the member surface portion. The fluidity means includes means emissive of a fluid which is flowable along at least a part of the member surface portion so as to be contiguous at least a part of the body surface portion when at least a part of the body surface portion communicates with at least some of the pin end surface portions. Typically, the pins are arranged and configured in such manner as to be capable of increasing the turbulence of the fluid which passes between the member surface portion and the body surface portion.
Many inventive embodiments provide a method for cooling an entity such as an electronic component. The inventive method comprises the folilowing steps: (a) providing a device having a device surface area and plural members which jut from the device surface area, the members having corresponding extremities opposite the device surface area; (b) associating the entity with the device, the entity having an entity surface area, the associating including placing the entity surface area in contact with at least some of the extremities; and (c) discharging fluid between the device surface area and the entity surface area so as to be disturbed by at least some of the members.
This invention meets all of the U.S. Navy""s requirements for dissipating/removing heat pursuant to its aforementioned power electronics program. The inventive heat sink: provides mechanical support to the module baseplate; is capable of dissipating heat from high power density devices; provides uniform cooling over the entire baseplate surface area; is small, lightweight and compact; and, carries relatively low manufacture and assembly costs.
The term xe2x80x9cpin,xe2x80x9d as used herein in relation to the present invention, refers to any member of any shape resembling or suggesting that of a rod, pole, staff, peg, post or pin, wherein the member juts, protrudes or projects, in post-like fashion, from a substrate. In accordance with many embodiments of the present invention, the pins may be made of a thermally conductive material such as metal, thereby complementing heat convection by the working fluid with heat conduction by the pins.
However, it was desirable for the U.S. Navy to reduce, minimize or eliminate metallic material in the heat sink assembly. In accordance with many embodiments of the present invention, the inventive post-like pins conduct no heat; the pins are made of a thermally nonconductive material such as plastic. According to some such inventive embodiments, the foundation section from which the pins project are also made of a thermally nonconductive material such as plastic; many such embodiments provide an integral thermally nonconductive structure comprising a foundation section and plural pins projecting therefrom.
According to inventive embodiments which thus implement thermally nonconductive pins, there is no significant or appreciable thermal conductivity; all or practically all of the heat which is removed from the to-be-cooled object is removed via convection, wherein the cooling fluid comes into direct contact with a surface or surface portion of the to-be-cooled object. A thermally nonconductive material will generally be a nonmetallic material; hence, the undesirable presence of metallic material in the heat sink, and the corrosion problems that are associated therewith, are advantageously eliminated by the present invention.
For instance, in inventive applications involving a module having a dielectric (e.g., ceramic) baseplate, the entirety of the heat is removed through the baseplate by the working fluid (e.g., water or air). The invention""s pins serve as mechanical support for the ceramic baseplate and to enhance the turbulent flow of the working fluid; the turbulent flow increases the heat-removal effectiveness of the working fluid. The present invention not only provides support for the baseplate to prevent breakage, but also cools the baseplate uniformly over the baseplate""s surface area. By virtue of its patterned pin configuration, the present invention""s performance is uniform, consistent and predictable.
The mechanically supportive functionality of the invention""s pins beneficially obviates the need for a xe2x80x9cthermal interfacexe2x80x9d or other means of attachment of a heat sink with respect to the item to be cooled. The present invention thus avoids the conventional need to furnish attachment-purposed structure, which is counterproductive to efficiency. Therefore, as compared with conventional heat sink methodologies in general, the present invention is simpler and more cost-effective to manufacture, since nothing is required to be attached to the module baseplate.
It should be understood that, according to this invention, the pins do not necessarily project from the heat sink""s base section. Key inventive features are that the pins are interposed between the object to be cooled, a heat sink surface bounds the working fluid flow on one side, and a to-be-cooled object surface bounds the working fluid flow on the opposite side. In inventive practice, the pins can project from either (i) a baseplate which is part of a module for holding an electronic component, or (ii) a base section which is part of the heat sink device, this base section itself representing a sort of xe2x80x9cbaseplate.xe2x80x9d
The invention can thus operate regardless of which of two opposing substrates the pins project from, viz., an object surface (e.g., a xe2x80x9cmodular baseplate surfacexe2x80x9d) or a heat sink surface (e.g., a xe2x80x9cheatsink baseplate surfacexe2x80x9d). Therefore, according to many embodiments, a cooling assembly comprises a modular baseplate, a heatsink baseplate, plural pins and a replenishable fluid. The pins connect the modular baseplate and the heatsink baseplate. The replenishable fluid is disposed between the modular baseplate and the heatsink baseplate so as to be disrupted by at least some of the pins. Such inventive arrangements can prove especially propitious for applications involving high heat fluxes, wherein the modular baseplate (and perhaps the rest of the module, as well) is made of a dielectric material, e.g., a nonmetallic material such as ceramic, and thereby affords electrical isolation to the electronic component which is housed by the module.
Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
The following appendices are hereby made a part of this disclosure:
Attached hereto marked APPENDIX A and incorporated herein by reference is the following conference presentation (58 pp): Michael Cannell, Roger Cooley, Joseph Borraccini, xe2x80x9cNSWC PEBB Hardware Development Progress,xe2x80x9d presented at the PEBB Design Review in Charleston, S.C., Jan. 27, 1999. See, especially, the pages therein entitled xe2x80x9cPEBB Thermal Management.xe2x80x9d
Attached hereto marked APPENDIX B and incorporated herein by reference is the following conference presentation (28 pp): Pete Harrison, Richard Garman, Joseph Walters, xe2x80x9cPEBB Thermal Management,xe2x80x9d presented at the PEBB Design Review in Charleston, S.C., Jan. 27, 1999. See, especially, pages 21 through 27.
Attached hereto marked APPENDIX C and incorporated herein by reference is the following conference paper (17 pp): Richard Garman, xe2x80x9cPEBB Thermal Management using ANSYS Multiphysics,xe2x80x9d ANSYS User""s Conference, Jun. 10, 1999.
Attached hereto marked APPENDIX D and incorporated herein by reference is the following conference presentation (24 pp): Richard Garman, xe2x80x9cPEBB Thermal Management using ANSYS Multiphysics,xe2x80x9d presented at the ANSYS User""s Conference, Jun. 10, 1999.
Attached hereto marked APPENDIX E and incorporated herein by reference is the following informal paper (11 pp, including several photographs): Michael Cannell et al., xe2x80x9cNSWC Manifold Installation,xe2x80x9d which discloses an assembly procedure for the turbulence enhancing support pins heat sink, in accordance with the present invention.
Attached hereto marked APPENDIX F and incorporated herein by reference are the following drawings (presented herein as two sheets, representing one large sheet): Dr. Peter N. Harrison et al., fabrication drawings for the turbulent enhancing support pins heat sink manifold, in accordance with the present invention.